1. Field of the Invention
This invention relates to a head displacement measuring method, a data recording/reproducing method, a head displacement measuring apparatus and a data recording/reproducing apparatus, for example, for a magnetic disk device in which a recording head for recording data on a magnetic disk and a reproducing head for reproducing data from the magnetic disk are separately provided.
2. Description of the Related Art
In some magnetic disk devices for recording data on a disk-shaped recording medium, such as, a magnetic disk, and reproducing data from the magnetic disk, a so-called magneto-resistive (MR) head is employed as a reproducing head to improve reproduction sensitivity. In such magnetic disk device having an inductive recording head and an MR reproducing head, the reproducing head is set to be smaller in width than the recording head, that is, the width of the reproducing head is made smaller than the width of a track formed by scanning on the magnetic disk by the recording head. Thus, even when the recording head and the reproducing head are integrally formed with centers thereof displaced from each other and therefore when the center of the reproducing head is displaced from the center of the track formed by the recording head operational problems do not emerge.
With this technique, however, since the width of the recording head must be designed to be redundantly large, the recording density cannot be increased.
Thus, there is a magnetic disk device which reduces the redundancy in designing and realizes higher recording density by equalizing the width of the recording head and that of the reproducing head, then optically measuring displacement of the center of the reproducing head from that of the recording head using, for example, a microscope, then supplying the displacement as an amount of correction (hereinafter referred to as offset) to a positioning (tracking) servo circuit, and adding or subtracting the offset to or from a position error signal (tracking error signal) indicating a position error to correct the tracking position of the recording head or the reproducing head. However, it is costly and time-consuming to measure the displacement of the center of the reproducing head from that of the recording head. In addition, the above-mentioned technique is not responsive to temporal changes.